The present invention relates to measuring apparatus, and more particularly to a method and device for at least approximately determining the cross-section of elongated objects, especially yarns, rovings and slivers in the textile industry, and of cables or filaments.
A number of methods and devices are already known for determining the cross-section of elongated objects, such as yarns, rovings and silvers in the textile industry, and of cables or filaments. These known methods and devices are based on various physical principles. Those which have proved especially apt have been electro-optical and capacitive methods, and in recent times electro-acoustical methods, and these have resulted in a diversity of measuring systems.
The above-mentioned electro-acoustical methods have, however, not yet found widespread acceptance since the control of the sonic fields and evaluation of their variations resulting from the test object affecting their undisturbed propagation require extensive research into the most effective arraangement.
A first proposed solution for influencing an acoustic field by elongated objects consisting of fibers, especially yarns, rovings and slivers, and of cables or filaments, is to be found in my U.S. Pat. No. 3,750,461, issued on Aug. 7, 1973. There, the elongated object, hereinafter referred to as the test object, is passed through the zone of oscillation nodes or antinodes of a standing wave with the standing wave being propagated from resonance generators and aimed at the test object. The presence of the test object acts upon the standing wave in the sense of affecting the pulse timing or phase at the point of arrival of the test object, so that from the size of this change (by comparison with undisturbed propagation), it is possible to determine the cross-section of the test object.
A further development of this principle is disclosed in my U.S. Pat. No. 3,854,327, issued on Dec. 17, 1974. This describes a method in which the test object passes through a sonic field having two different frequencies, for example a basic frequency and double this basic frequency in superimposed sonic fields. In principle, one frequency would suffice, but it is advisable to use a second frequency in order to compensate for temperature effects and dirt deposits. In this regard, temperature changes and possible dirt deposits on the resonator walls affect the two frequencies relatively to approximately equal extents. The two frequencies may be emitted simultaneously at the sonic emitter or they may be emitted intermittently by means of commutation at the sonic emitter. In principle, measurement at one frequency alone may be adequate under most circumstances, for example. The second serves only to compensate interference sources which usually change slowly.
The electro-acoustic transducers acting as sonic emitters or sonic receivers are located on plane surfaces, the space between them being exposed or open to the atmosphere. The sound pressures existing in the standing wave then relate to the environmental atmospheric pressure.
Also this method and the corresponding apparatus are not free from limitations relating to their application. There are spinning techniques in which the test object (fibrous material) is carried by compressed air through a duct from one processing stage to the next and determination of the amount of fibrous material or of the cross-section is to be performed in this duct zone, as it is not possible to provide a measuring unit at any other place. However, the use of compressed air prohibits the passage of the test object through a test unit which is open at one or both sides.
Furthermore, measuring units operating on the principles explained above cannot be applied if they are mounted directly onto production machines. The measuring units tend to be undesirably shaken by the inevitable machine vibrations and there are no acoustic receivers which do not react unfavorably to such vibrations, especially as they must be built in the form of highly sensitive transducers.
Measuring units in accordance with the developments described as the state of the art can thus only be used with adequate precision in measuring apparatus set up at undisturbed locations (e.g. in laboratories) and provided for measuring test samples away from the production line. However, modern technologies demand constant monitoring directly during the production process in order to perform the necessary control and regulation of functions without delay on the basis of the test results.